Dear Authors, please find my comments in the attached PDF file.

This work investigates the highly relevant question of the seasonal dynamics of water transfers in shallow soils (<60 cm depth)  in an alpine grassland context. In particular, this work aims to distinguish between the seasonality of water available for vegetation and the water that percolates vertically to recharge groundwater. Isotopic transfers are modeled using the HYDRUS-1D model. Meteorological data are measured locally, and samples for isotopic analyses are collected monthly.

I mainly have a few substantive comments on this work, which is overall comprehensive:

• The use of snow depth measurements to estimate melt flux is very simplistic. Indeed, this does not account for processes such as compaction, refreezing, stratification, etc. Snow sublimation is not mentioned. The degree-day model is simplistic and poorly represents these fluxes. Is sublimation accounted for in the calculation of AET in winter? There are instrumental methods for directly calculating melt flux ( see Eeckman et al., 2025).
  
  This point could be specified in the “dataset” paragraph or in the discussion.
• The issue of rain-on-snow is not addressed: how does the degree-day model respond in this case? There could perhaps be specific thresholds for such conditions. Have you observed this situation in your meteorological data? This is a very important point for estimating melt flux, especially in spring.
• How do you consider lateral transfers? In steep slope contexts, infiltration upstream can be transferred laterally at shallow depths (<60 cm) and re-emerge downslope to supply the root zone again. In these specific contexts, infiltration at the bottom of the soil column does not necessarily lead to groundwater recharge or streamflow contribution.

Minor remarks:

• l. 99 “In Swiss catchment”: please provide references and/or describe which catchments.
• Figure 1: how is the AET presented in this figure calculated?
• l. 245: do you have a reference for this thermal lapse rate in the region?
• l. 310: eq. 2.7, 2.8: please provide references for these equations.
• Figure 7: the measured and simulated data are not distinguishable in the figure.
• Figure 8: there are many overlapping curves. Could these be separated into multiple panels for better readability?
• Figure 12: specify the variables simulated with HYDRUS-1D.